Update to cache V4 in workflows

Author: kklamberty

.github/workflows/arraymerge_gtest.yml

@@ -18,7 +18,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Cache gtest library
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       env:
         cache-name: cache-gtest-lib
       with:

.github/workflows/arraymerge_test_valgrind.yml

@@ -18,7 +18,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Cache gtest library
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       env:
         cache-name: cache-gtest-lib
       with:

.github/workflows/mergesort_gtest.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Cache gtest library
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       env:
         cache-name: cache-gtest-lib
       with:

.github/workflows/mergesort_test_valgrind.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Cache gtest library
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       env:
         cache-name: cache-gtest-lib
       with: